Based purely on the number of horror stories on this board, and availability heuristic aside, you might want to have them clearly spell out what happens if they royally @#$% up. If it still reeks and off-gasses months later, or any number of other things that commonly go wrong, what's the resolution and their responsibility? Sorry but I wouldn't want to be stuck in the middle of "I installed it right, the product is to blame," vs. "My product is fine, the installer just @#$%ed up," and be left holding the bag and unable to use the space. If people aren't willing to spell out their obligations in such a scenario, maybe find more accountable people to work with.